1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display device.
2. Description of the Related Art
Today, a transflective liquid crystal display device provided with both reflective and transflective display capabilities is now being developed. The transflective liquid crystal display device is arranged to reduce the power consumption in a bright environment by turning off its backlight unit and to allow a user to view an image on the screen in a gloomy or dark environment by turning on the backlight unit. It means that the transflective liquid crystal display is fitted to portable instruments such as a portable phone and a digital camera to be used in many kinds of illuminating environments.
The transflective liquid crystal display device is required so that a transmissive area and a reflective area are individually located in each pixel and each area is designed to have the optimal retardation value. This design can be achieved by making the reflective area stepped and the thickness of the liquid crystal layer of the reflective area about half as long as the thickness of the liquid crystal layer of the transmissive area. Further, to make the optical characteristic of the transmissive area equal to that of the reflective area, the transflective liquid crystal display device is also required to have a retardation film of a λ/4 plate (where λ is a wavelength of light).
The technique of the retardation film has been disclosed in JP-A-2003-279956 and JP-A-Hei5-100114. JP-A-2003-279956 discloses a composition in which a retardation film is built in a liquid crystal cell. JP-A-Hei5-100114 discloses a composition in which a combination of a λ/2 plate and a λ/4 plate is served as a wide circular polarization plate.
Further, another technique of building the retardation film in a reflective TN (Twisted Nematic) system liquid crystal display device has been disclosed in JP-A-2004-205801. JP-A-2004-205801 proposes a method of adjusting a retardation value of a built-in retarder plate according to each color pixel so that the retardation may be λ/4 in each wavelength.
The transflective liquid crystal display device of an ECB (Electrically Controlled Birefringence) system, a VA (Vertical Alignment) system or a TN system is requested to build the retarder plate in it from viewpoints of reduction of coloring when displaying a reflected black image, a high reflective contrast ratio, and thinning. Disadvantageously, these prior art documents do not disclose a way of building the retarder plate in a transflective liquid crystal cell and thus do not bring about a sufficient reflective contrast and so forth.